Blood (Serum) Potassium Test

What is the blood potassium test?

This test measures the amount of potassium in your blood. Potassium is one of several elements in blood called electrolytes. Potassium is very important for normal heart and nervous system function. For example, a high blood level of potassium can lead to serious and even fatal heart rhythm problems.

Why is this test done?

The serum potassium level is usually measured with several other blood factors to look for certain diseases. The test can be helpful in evaluating disorders of the heart, kidneys, adrenal glands, muscles, and digestive system.

This test may also be done to check certain medical treatments. Some medicines can cause the body's potassium level to go up or down. Some medicines, such as digitalis, don't work well if your potassium level isn't normal.

How do I prepare for this test?

• You don't need to fast or limit your activity before the test.
• You may need to avoid taking certain medicines before the test because they might affect the test result. Make sure your health care provider knows about any medicines, herbs, or supplements that you are taking. Don't stop any of your regular medicines without first consulting with your health care provider.
• Talk to your health care provider if you have any questions.

How is the test done?

A small amount of blood is taken from your arm with a needle. The blood is collected in tubes and sent to a lab.

Having this test will take just a few minutes of your time. There is no risk of getting AIDS, hepatitis, or any other blood-borne disease from this test.

How will I get the test result?

Ask your heath care provider when and how you will get the result of your test.

What does the test result mean?

The normal potassium range for adults in most labs is 3.5 to 5.5 milliequivalents (mEq) per liter. This range may vary slightly from lab to lab. Normal ranges are usually shown next to your test result in the lab report.

Your blood level of potassium may be higher than normal because:

• Your kidneys or adrenal glands aren't working well.
• You have internal bleeding.
• You are taking certain types of blood pressure medicines that cause the body to hold onto extra potassium. ACE inhibitors and potassium-sparing diuretics, such as spironolactone, are examples of these medicines.

Sometimes red blood cells break as they pass through the needle into the blood-collecting tube. The cells may release potassium when this happens and cause your test result to be high, even though the level of potassium in your body is normal. When this happens, your health care provider may ask you to repeat the test.

Your serum potassium level may be lower than normal because:

• You have had a lot of vomiting or diarrhea.
• You are taking certain medicines, such as water pills (diuretics), that cause your body to lose potassium.
• You are not getting enough potassium from your diet.
• You have been sweating heavily during exercise.
• You have kidney, liver, heart, or adrenal (glandular) disease.

What if my test result is not normal?

Test results are only one part of a larger picture that takes into account your medical history and current health. Sometimes a test needs to be repeated to check the first result. Talk to your health care provider about the results and ask questions.

If your test results are not normal, ask your health care provider:

• if you need additional tests
• what you can do to work toward a normal value
• when you need to be tested again.